JPH0711056B2 - Die steel manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a die steel, and more particularly to a method for producing a cold die steel having extremely few defects such as microvoids and inclusions.

(Conventional technology and problems) Cold die steel is an alloy tool steel used for cold dies such as wire drawing dies and press dies, and its chemical composition is specified in JIS SKD1, 2, 11, 12 etc. As described above, C is contained in a large amount, and alloy elements such as C and Cr form carbides, thereby providing sufficient wear resistance or toughness.

The melting process is usually performed by melting in an electric furnace and then performing in-furnace refining such as ladle refining to make ingots. Measures for high quality with few defects are taken.

However, nevertheless, the obtained cold die steel has many inspection defects by ultrasonic flaw detection, and there are microvoids and inclusions, especially large oxide inclusions. It adversely affects the required excellent mechanical properties, and the emergence of a remedy for it is desired.

(Object of the Invention) The present invention has been made in order to meet such melting, solves the above-mentioned drawbacks of the prior art, and provides a high-quality cold die steel with extremely few defects such as microvoids and inclusions. It is intended to provide a manufacturing method.

(Structure of the Invention) In order to achieve the above object, the inventors of the present invention analyzed the contents of defects such as micro voids and inclusions found in the cold die steel, and found that the peak value of ultrasonic flaw detection was 2 minutes. Is
Occurrence of inclusions on the high wave side (40% or more) and inclusions and micro voids on the low wave side were observed, and most of the inclusions were very similar to the powder component of the oxide film inhibitor used during agglomeration. Was obtained. Based on this, the cause of the above defects was investigated for each manufacturing process, and the countermeasures were examined.As a result, Al was added to promote the cleaning of molten steel and to prevent the generation of CO, and the pouring speed during casting was moderated. It was found that this is possible by preventing the oxide film inhibitor from being caught.
The present invention has been made here.

That is, the present invention, C: 0.80 ~ 2.00%, Si: 2.0% or less,
Mn: 2.00% or less and Cr: 4 to 16% as an essential component,
Furthermore, when steel containing 0.010 to 0.100% Al is melted, and when the molten steel is cast by the ingot casting method using an oxide film inhibitor, the pouring speed during casting is set to 200 mm / min or less. The gist is a method for manufacturing a cold die steel, which is characterized by the above.

The present invention will be described in detail below based on examples.

As mentioned above, cold die steel is produced by the steps of melting in an electrode furnace, ladle refining, and ingot casting.
By adding 0.100%, preferably 0.020 to 0.040%, it is effective in preventing the generation of small defects on the low peak value side, and it is possible to significantly reduce the number of inclusions and at the same time suppress the generation of microvoids in particular. . In this case, the amount of Al added is
If it is less than 0.010%, the above effect cannot be expected at all, and conversely 0.100.
%, The toughness of the cold die steel decreases, so it is necessary to add it in the range of 0.010 to 0.100%. In order to sufficiently suppress the effects of suppressing the generation of microvoids, significantly reducing inclusions, and toughness, it is preferable to add in the range of 0.020 to 0.040%.

By adding Al in this way, it is possible to reduce the generation of microdefects compared to the Al-free material, and the effect of Al deoxidation is clear, but the mechanism is not always clear, but Al ₂ O ₃ is generated and floated by the addition of Al to promote the cleaning of molten steel, and Al preferentially oxidizes Si, C, Cr, etc. to prevent the generation of CO gas and suppress the generation of microvoids. It is considered to be a thing.

Next, the inclusions found in Al-added cold die steel are very similar to the powder component of the oxide film inhibitor used in the ingot casting, so the inclusion of powder by high-speed injection of molten steel is prevented. For this reason, it is necessary to regulate the rising speed of the molten metal during pouring and gradually raise the molten metal surface. According to the experiment, the smaller the rising speed is, the more the inclusions, especially the large inclusions can be eliminated if it is 200 mm / min or less. On the contrary, when the rising speed exceeds 200 mm / min, the powder is rapidly wound. It was found that the inclusions caused large inclusions in the ingot. In order to prevent the entrainment of powder, it is preferable to place the oxide film inhibitor on the bottom rather than suspend it in the mold.

The above manufacturing process can be applied to various steel grades in which a predetermined amount of Al is added to the steel grades specified in JIS SKD1, 2, 11, 12, etc. Cold die steel in C: 0.80-2.00%, Si: 2.00%
Hereinafter, the steel contains Mn: 2.00 or less and Cr: 4 to 16% as essential components, further contains Al in an amount of 0.010 to 0.100%, and has significantly reduced microvoids and inclusions.

Although the above-mentioned added amount of Al is for the above-mentioned reason, within the range of the added amount, the impact resistance and the wear resistance are equivalent to those of the conventional steel, and there is no particular problem in the characteristic value as the cold die steel. The limitation of the above essential components is almost the same as that of conventional steel, and
The addition of Cr and Cr in the above range is to form carbides and improve the wear resistance, and the above upper limits of Si and Mn are defined to prevent the deterioration of toughness. In addition, one or more of Mo, W, V, Co, and Nb are added as optional additives in a total amount of 5% or less to improve impact resistance, wear resistance, hardenability, toughness, etc. Can be planned.

(Example) C: 1.5%, Si: 0.3%, Mn: 0.5%, Cr: 11%, Mo: 1% and V:
Molten steel containing 0.3% and further added with the amount of Al shown in Table 1 was prepared by ladle refining and then ingot-casting was obtained. The surface antioxidant used during the agglomeration has a composition of 50% Si-40% Al ₂ O ₃ -10% CaO.

Rolling each of the ingot (3t) in 110Mmfai, the rolled material subjected to ultrasonic flaw detection (sensitivity _{V 1 · 5-2 · 0 = 80} %), was cut in the case of finding a defect portion, the micro test A mirror was used to distinguish between microvoids and inclusions, and the number of them was examined. The results are shown in Table 1.

As is clear from Table 1, the Al content of cold die steel
When the content is 0.010% or more, the generation of microvoids can be particularly suppressed, and large inclusions can be considerably reduced. However, when the pouring speed during casting is 200 mm / min or less, large inclusions can be eliminated. A Charpy impact test and a wear test were performed on each steel, and both the impact resistance and the wear resistance were the same as those of the conventional steel containing no Al.

(Effects of the Invention) As described in detail above, according to the present invention, by adding an appropriate amount of Al, and by controlling the pouring speed at the time of casting in the bottom casting method using an oxide film inhibitor, Cold die steel with very few defects such as micro voids and inclusions can be manufactured, and the addition of Al does not adversely affect the characteristic values such as impact resistance and wear resistance, so it is possible to produce high quality cold rolled steel with excellent characteristics. The inter die steel can be provided.

Claims (1)

[Claims] 1. In weight% (hereinafter, the same), C: 0.80 to 2.00
%, Si: 2.0% or less, Mn: 2.00% or less and Cr: 4 to 16% as essential components, and further melted steel containing 0.010 to 0.100% Al, and melted the molten steel with an oxide film inhibitor. When pouring by using the lower casting method, the pouring speed at the time of pouring is 200 mm / mi
A method for producing a cold die steel, which is characterized in that it is n or less.